Anaerobic sludge digestion is an effective process for treating biosolids in large municipal wastewater treatment plants. Following digestion, the sludge is dewatered, and the resulting centrate or filtrate is returned to the main treatment system. However, this stream presents a significant challenge due to its elevated ammonia levels, typically ranging from 800 mg/L to 1,200 mg/L. In facilities that utilize thermal hydrolysis (THP) prior to anaerobic digestion, ammonia concentrations can be even higher. Additionally, high levels of BOD and COD are common, particularly in plants employing THP, further complicating treatment.

This recycle flow increases the ammonia and total nitrogen loading to the primary plant treatment process by up to 25% while adding only about 1% to 2% to the plant influent flow.

The recycle flow can be detrimental to plant design/operations in several ways:

• The recycled nitrogen load not only increases the aeration requirement to achieve nitrification but also adversely impacts the stability of the treatment process.
• It requires more process tank volumes.
• It can require adding an external carbon source, such as methanol, to achieve low total nitrogen limits.
• The increased oxygen requirements and additional chemical consumption contribute significantly to facility energy consumption and operational costs.
• When the biological activity slows in cold climates, the extra ammonia load can cause the treatment plant to exceed the NPDES permit limits, especially when stringent.

Veolia’s ANITA™Mox Deammonification Process

Veolia’s ANITA^™Mox process effectively treats the recycle flow from anaerobic digesters with high ammonia concentrations and solves the problems of returning high ammonia concentrations to the main plant treatment process. In addition, it helps save energy and O&M costs by reducing the demand for aeration and chemicals.

Veolia/Kruger is a leading provider of media-based deammonification solutions for the U.S. municipal market. Their ANITA™ Mox process offers two configurations—MBBR (Moving Bed Biofilm Reactor) and IFAS (Integrated Fixed Film Activated Sludge)—to deliver a single-stage de-ammonification using anammox bacteria. This process achieves over 90% ammonia removal and 75-85% total nitrogen removal, all while using significantly less energy than traditional nitrification-denitrification processes and without the need for an external carbon source.

Anammox Bacteria

The anammox bacteria, discovered in wastewater sludge in the early 1990s, exists naturally in marine and freshwater habitats. The word anammox was derived from ANoxic AMMonia OXidizing bacteria. They are unique in their ability to oxidize ammonia and reduce nitrite to produce nitrogen (N₂) gas.

The ANITA™ Mox process utilizes anammox bacteria to convert ammonia to nitrogen gas. It is performed in two steps: aerobic nitritation and anoxic ammonia oxidation. Anammox bacteria provides many advantages over traditional nitrogen removal processes, especially in treating ammonia-rich waste streams.

ANITA^™ Mox: MBBR Configuration

The two steps take place within a one-stage biofilm system, with nitrification (aerobic) occurring in the outer biofilm layer and anammox (anoxic) in the inner layer on the media carriers. This is accomplished in a single MBBR reactor tank, where conditions such as temperature, pH, and oxygen levels are precisely controlled to support the growth of anammox bacteria as a biofilm on AnoxKaldnes media carriers. The biofilm’s secure attachment to the protected areas of the carriers allows for long sludge ages, compensating for the slow growth rate of anammox bacteria. This makes the ANITA™ Mox system a simple, stable, and robust de-ammonification technology. The system also retains all the proven benefits of MBBR technology, including easy media carrier and biomass retention, maintenance-free SS air grids and media retention screens, and a straightforward flow-through design.

Benefits of MBBR ANITA^™ Mox

• Biofilm is resistant to flow and load variations and not prone to anammox washout.
• Simple and stable flow-through process.
• Easy to operate and maintain.
• The operator-friendly process does not require a champion operator.
• Media, aeration grids, and media retention screens are maintenance-free.
• Easy to expand capacity by addition of media.
• Tolerates high influent TSS influent without requiring pretreatment and therefore provides CAPEX savings.
• Do not require micronutrients, antifoaming, or other special agents.
• It can be in idle mode without feed for extended periods.
• Recovers quickly from process upsets such as power shutdowns, overfeed, under aeration…etc.
• The process tolerates temporary limitations or fluctuations in pH, temperature, and parameter concentrations.
• HDPE carriers last the life of the system.
• The Anita Mox process is proven to withstand short-term and prolonged system shutdowns. The system can be placed into low-flow or low-loading mode. This allows the facility to have flexibility in dewatering schedules and perform routine or emergency maintenance to their digesters or dewatering equipment without significantly impacting system performance.
• Anita Mox is the best technology for treating centrate/filtrate. 

ANITA^™ Mox: IFAS Configuration

The IFAS (Integrated Fixed Film Activated Sludge) configuration of the ANITA Mox process combines biofilms attached to media carriers and mixed liquor suspended solids (MLSS) and offers distinct benefits.

In the ANITA™ Mox IFAS system with anammox biofilms attached to media carriers, the MLSS concentration is maintained using a small sludge settling zone. The nitritation step, or the conversion from ammonia to nitrite, occurs in the MLSS. The de-ammonification step occurs mostly in the biofilm attached to the media carriers. Nitrite production is the limiting step in anammox conversion rates. Moving the nitritation step to the suspended phase increases nitrite production, thus providing an overall increase in anammox conversion and removal rates.

Added benefits of IFAS ANITA™ Mox include the following:

• Nitrogen removal rates are over two times higher
• Reduced footprint
• Lower dissolved oxygen levels are required, further improving energy savings.
• Handles the presence of high influent and potentially recalcitrant COD and other toxic substances better
• Best suited for centrate/filtrate treatment from anaerobic digesters following THP and treating food waste

ANITA^™ Mox Carriers

The ANITA™ Mox process hinges on a crucial component: the AnoxKaldnes carriers. These carriers offer a generously large and sheltered surface area for the biofilm to attach, creating optimal conditions for biological activity when suspended in water. Their design plays a pivotal role in enhancing oxygen and substrate transfer efficiencies by maintaining an ideal media bed depth. If the bed is too shallow, it compromises biofilm protection and attachment ease. Conversely, if it’s too deep, liquid mixing and biofilm scouring become challenging, leading to reduced oxygen and substrate transfer efficiencies and overall performance.

What sets these carriers apart is their unique design, enabling the retention of anammox bacteria within the reactors. This design significantly mitigates the risk of anammox washout, a problem commonly encountered in other suspended growth technologies. By minimizing this risk, the AnoxKaldnes carriers contribute significantly to the efficiency and stability of the ANITA™ Mox process.

Conclusion

Municipal wastewater treatment plants (WWTPs) are facing increasingly stringent effluent limits, driving the need for cost-effective solutions to reduce ammonia and total nitrogen (TN) levels. Among these options, the ANITA™ Mox process stands out for its unique advantages and cost-efficiency, making it one of the most widely adopted de-ammonification technologies for treating centrate and filtrate from anaerobic digesters. This process effectively reduces ammonia and TN in the recycled water returning to the main treatment system.

Leading the delivery of this media-based de-ammonification solution to the U.S. municipal market is Veolia/Kruger. The Veolia U.S. team works closely with Veolia’s Engineering and Research Institute in France and AnoxKaldnes AB in Sweden, ensuring the technology incorporates the latest innovations and expertise.

Over the past decade, the ANITA™ Mox process has been implemented in more than 35 full-scale facilities. It successfully treats centrate, filtrate, and pressate from both conventional anaerobic digesters and those using thermal hydrolysis processes (THP). This widespread adoption highlights the technology’s proven reliability and effectiveness in meeting the stringent demands of modern wastewater treatment.

Veolia’s ANITA™ Mox process is the most dependable sidestream de-ammonification solution on the market, offering versatile configurations and distinct benefits for municipal WWTPs.

4o

Contact Envirep

Envirep/TLC serves the municipal and industrial water and wastewater market in Pennsylvania, New Jersey, Maryland, Delaware, the District of Columbia, Virginia, and West Virginia.

Do you need help selecting the right equipment for your application? Contact Envirep at 717-761-7884 or sales@envirep.com.

By Michael Gillespie, President at Envirep/TLC